1. Field of the Invention
The present invention relates to a process of producing a grating to be used in an X-ray image pickup apparatus.
2. Description of the Related Art
Recently, an image pickup method utilizing Talbot interference (Talbot interferometry) has been investigated as an imaging method utilizing X-ray phase contrast (X-ray phase imaging). In the image pickup apparatus utilizing Talbot interference, X-ray radiation emitted from a spatially-coherent X-ray source passes, in sequence, through a subject, a pair of diffraction gratings arranged in accordance to principles of Talbot interferometry, and reaches a detector to form an image. Specifically, X-ray radiation after passing through a subject is made incident on a diffraction grating for periodically modulating the phase of the X-ray (hereinafter, referred to as phase grating), and a diffraction grating made of a material absorbing the X-ray and having a sufficient thickness (hereinafter, referred to as absorption grating), so that X-ray phase imaging is performed. Conventional X-ray imaging, whether measured with film or digital detectors, relies in the absorption of X-ray radiation, e.g., in tumorous versus healthy tissue. Accordingly, there are limitations in conventional absorption radiography due to tradeoffs between contrast and dose. In contrast, X-ray phase imaging is believed to be advantageous due to an excellent sensitivity to soft structures; and great spatial resolution limited only by the pitch of the gratings.
In this specification, the term “spatially-coherent X-ray source” refers to an X-ray source that can generate X-ray radiation having coherent wavefronts in the direction of the X-ray propagation. In general, an X-ray source produces fan-shaped or cone-shaped X-ray beams. The thus generated X-ray radiation enters a grating at a certain radiation angle. Therefore, the direction of the incident X-ray beams is not parallel to the direction of grooves formed in the grating, and thereby a shadowed area is formed. As a result, a clear image cannot be easily captured.
FIG. 3 illustrates a known method of using a grating that is curved at the same curvature of the coherent wavefronts of fan-shaped or cone-shaped X-ray beams. When the curved grating is used, the direction of incident X-ray radiation is parallel to the direction of grooves formed in the grating, and thereby a clear image can be obtained.
FIG. 4 illustrates a known method for realizing such a curved grating. As shown in FIG. 4, a curved state of a grating 401 can be maintained by applying force 403 to supporting elements 402 (See, Japanese Patent Publication Laid-Open No. 2007-206075).
However, in the method shown in Japanese Patent Publication Laid-Open No. 2007-206075, it is necessary to continuously apply force to the grating for maintaining the curvature while the grating is irradiated with X-ray radiation. Otherwise, the grating cannot maintain the curvature and returns to a non-curved state, whereby the quality of image detection can be negatively affected. Thus, the known grating structure lacks shape stability.